This invention relates to the field of prefabricated door frames. Such door frames are customarily assembled by a manufacturer and shipped intact to a builder's supply store or other sales outlet. These door frames must fit a wide range of wall thicknesses which may vary from four and nine-sixteenth inches when the studding is made of 2.times.4's to something in excess of six and one-half inches for 2.times.6 studding, and sometimes considerably more, depending upon the climate of the locality.
It has been the past commercial practice to supply prefabricated door frames in a size which is at least of the proper size to fit the minimum four and nine-sixteenths inch wall thickness, to which other pieces can be added for thicker walls, or unitary door jambs may be used which are made from the wider stock necessary to fit thicker walls. Prefabricated door frames at best involve substantial shipping cost, because such frames cannot be stacked inside each other, and since they thus enclose a substantial volume of air, they occupy correspondingly substantial volume in a truck trailer. The shipper must therefore pay for transporting the empty space inside of each such prefabricated door frame.
It is therefore apparent that there is a need to provide prefabricated door frames which may be stacked more compactly and which readly accommodate a variety of wall thicknesses.